All kinds of micro-organisms exist around us, and, in some instances, interfere with our ability to live healthy lives. Micro-organisms present in our clothing can multiply rapidly because the conditions are favorable due to the heat, humidity and available nutrients. Therefore, it has been very desirable to provide fibers that have antimicrobial activity to protect both the user and the fibers, and to do this economically. For convenience herein, the expression "antimicrobial" is used generally to include antibacterial, antifungal, and other such activity.
Proprietary antimicrobial acrylic and acetate fibers are currently commercially available. However, because polyester fibers have been the synthetic fibers that have been produced and used in the greatest quantities for many years, it would be desirable to have a polyester antimicrobial fiber with improvements over the existing commercially available acrylic and acetate antimicrobial fibers. Since only the antimicrobial agent on or near the surface of a fiber contributes to its antimicrobial effect, it has been considered desirable to provide as much of the antimicrobial agent as possible close to the peripheral surface of the fiber. Thus, it would be desirable to provide an antimicrobial polyester fiber where the antimicrobial agent is disposed in the sheath of a bicomponent sheath-core fiber, since the sheath is disposed near the surface of a fiber. Moreover, since antimicrobial agents are relatively expensive, it would be desirable to use as little of the agent as possible. Therefore, it would be desirable to make the sheath as small as possible. Although bicomponent antimicrobial polyester fibers have been suggested many times in the prior art, as will be related hereinbelow, so far as is known, a satisfactory polyester bicomponent antimicrobial fiber has not been commercially available.
Much effort has been directed at embedding metal ions, which have long been known to have an antimicrobial effect, in polymers to give antimicrobial activity in fibers. This effort in particular has been directed to incorporating metal containing zeolites into the polymer. For instance, Jacobson et al. in U.S. Pat. Nos. 5,180,585 (1993), 5,503,840 (1996) and 5,595,750 (1997) discloses the use of an antimicrobial composition comprising zeolites. However, Jacobson recognizes the problems of color deterioration associated with high metal loadings, as for example, experienced by zeolites, and instead proposes an antimicrobial composition which does not experience this problem, especially when incorporated in a polymer matrix.
In addition, the use of zeolites in sheath-core fibers is known. Hagiwara et al., in U.S. Pat. No. 4,525,410 (1985), discloses packed and retained metal zeolites in a mixed fiber assembly, such as sheath-core composite fibers, including polyester fibers (see col. 5, line 50 et seq.). Japanese Published Application Kokai No. Sho 62-195038 (1987, Kanebo, et al.) prepared polyester molded products from a hydrophilic substance and a polyester to retain metal zeolite particles, and suggested spinning conjugate sheath-core fibers. Hagiwara et al., U.S. Pat. No. 4,775,585 (1988), disclosed bactericidal metal ions at ion-exchange sites of zeolite particles in polymer articles, including fibers having a sheath-core structure (see col. 9, lines 3-6), and including conjugated yarns of polyethylene terephthalate; (see Example 2 in col. 14). Ando et al., in U.S. Pat. No. 5,064,599 (1991) included such ions at such sites in a low-melting component of conjugate fibers, including polyester components (see Examples 1 and 2). Nippon Ester, Japanese Published Application Kokai No. Hei 8 (1996)-120524, suggested a hollow sheath-core polyester fiber with a subliming insecticide in the hollow core polyester and a zeolite in the sheath polyester. Nakamura Kenji, Japanese Published Application Kokai No. Hei 9-87928 (1997) also suggested a sheath-core polyester fiber with a metal zeolite in the sheath. However, it has been found that the use of certain zeolites may produce unacceptable polymer and fiber degradation. See, for example, Sun-Kyung Industry (Ltd.), Korean Publication No. 92-6382 (1992), (hereinafter referred to as the Korean Publication) which discloses that zeolites have the capability to absorb or release water, and therefore degrade the properties of polyester fiber, which is easily hydrolyzed by water.
None of the patents or publications discussed above discloses a sheath comprising a relatively small percentage of the total cross-sectional area of the fiber. In fact, the Korean Publication discloses that it has been advisable not to reduce the amount of sheath below 30% of the cross-sectional area of the fibers in order to obtain good processing and physical properties. In particular, the Korean Publication discusses that if the sheath is less than 30% of the cross-sectional area of a fiber, the core may shift in one direction and protrude from the fiber surface to lower the antimicrobial effect of the fiber. In addition, when the sheath comprises more than 70% of the total fiber cross-sectional area, it is difficult to position the core component at the center of the fiber during spinning, and therefore the antimicrobial properties of the fiber cannot be improved further. This warning was confirmed by Teijin in Japanese Published Applications Kokai Nos. Hei 6-228,823 (1994) and Hei 7-54208 (1995), namely that the sheath-core weight ratio should be 30/70 to 70/30, or the sheath component would tend to break and spinning productivity would drop. Thus, Teijin preferred especially a sheath-core ratio of 45/55 to 55/45.
In addition, when an antimicrobial agent relies on the hydrophilic nature of a zeolite to impart antimicrobial properties, the use of a hydrophobic slickener on the fiber is precluded. Hence none of the patents or publications discussed above discloses use of a slickener with an antimicrobial agent, where the antimicrobial agent is added to the polymer during fiber manufacture, so that the agent is embedded in the fiber. It is known to apply an antimicrobial agent and a slickener to a fiber after the fiber is produced. However, this does not produce a fiber with a durable slickener or antimicrobial agent. Hence, there are no known commercially available antimicrobial fibers having an antimicrobial agent added during fiber manufacture, with a slickener applied to the surface of the finished fiber.
For all the reasons discussed above, it would be desirable to produce an antimicrobial polyester fiber which has effective antimicrobial properties, but which is not expensive to produce. In addition, it would be desirable to produce an antimicrobial polyester fiber which does not experience the problems of the prior art of discoloration and degradation, as well as those associated with spinning productivity. Moreover, it would be desirable to produce an antimicrobial polyester fiber having an antimicrobial agent added during fiber manufacture which fiber may be slickened.